Optical transmission systems frequently includes sections of optical fibers connected end-to-end to transfer light from one fiber to another. In such systems, it is desirable that the transfer of light between fibers be accomplished with little loss of signal; i.e., with low insertion loss. Insertion loss can result from several factors including the presence of a gap or separation between the ends of the connected fibers. Specifically, some light is lost if the end faces of two fibers are separated because light diverges as it radiates from the end of a fiber. In addition, fiber-to-fiber separation results in an insertion loss due to Fresnel reflections at the two glass-air interfaces between the spaced fibers.
Optical fibers are available in multi-mode and single-mode types. Multi-mode fibers have relatively high propagation losses. Because they are inherently lossy, some insertion loss at the interface of two connected multi-mode fibers can often be tolerated.
Single-mode fibers are manufactured such that propagation losses are significantly reduced. In single-mode systems, therefore, insertion losses at the interface of connected fibers must be minimized. In single-mode systems, accordingly, it is particularly important that the end faces of connected fibers be maintained in virtual contact with one another to minimize insertion losses due to fiber-to-fiber separation and Fresnel reflections.
Optical fiber connectors frequently include a rigid sleeve of ceramic or other hard material or a sleeve of resilient plastic, which supports the optical fiber and holds it rigidly in position within the connector. The fiber protrudes slightly from the end of the sleeve when manufactured, and it is necessary to polish the end face of the protruding fiber prior to incorporation of the connector into an optical transmission system.
Typically, the end face of the fiber was polished by mounting the connector to a polishing tool such that the end of the ceramic sleeve extended from a flat end surface of the tool. The tool was then moved over a polishing medium by hand until the end face of the protruding fiber was satisfactorily polished.
With known polishing tools, the polishing process was inconsistent, unpredictable manner. For example, the fibers were often polished to such an extent that the polished ends of the fibers because slightly recessed within the ceramic sleeve in which they were supported. The recesses resulted in a gap between connected fibers which, although often acceptable in multi-mode fiber systems, were unacceptable in single mode systems.
In general, known polishing tools required skilled personnel exercising substantial care to produce acceptably polished fibers.